ABSTRACT
Protein arginine methyltransferases (PRMTs) are responsible for symmetric and asymmetric methylation of arginine residues of nuclear and cytoplasmic proteins. In the nucleus, PRMTs belong to important chromatin modifying enzymes of immense functional significance that affect gene expression, splicing and DNA repair. By time-lapse microscopy we have studied the sub-cellular localization and kinetics of PRMT1 after inhibition of PRMT1 and after irradiation. Both transiently expressed and endogenous PRMT1 accumulated in cytoplasmic bodies that were located in the proximity of the cell nucleus. The shape and number of these bodies were stable in untreated cells. However, when cell nuclei were microirradiated by UV-A, the mobility of PRMT1 cytoplasmic bodies increased, size was reduced, and disappeared within approximately 20 min. The same response occurred after γ-irradiation of the whole cell population, but with delayed kinetics. Treatment with PRMT1 inhibitors induced disintegration of these PRMT1 cytoplasmic bodies and prevented formation of 53BP1 nuclear bodies (NBs) that play a role during DNA damage repair. The formation of 53BP1 NBs was not influenced by PRMT1 overexpression. Taken together, we show that PRMT1 concentrates in cytoplasmic bodies, which respond to DNA injury in the cell nucleus, and to treatment with various PRMT1 inhibitors.
Subject(s)
Cytoplasm/enzymology , DNA Damage , Gamma Rays , Protein-Arginine N-Methyltransferases/metabolism , Repressor Proteins/metabolism , Ultraviolet Rays , Animals , Chromosomal Proteins, Non-Histone/genetics , Chromosomal Proteins, Non-Histone/metabolism , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , HeLa Cells , Humans , Intracellular Signaling Peptides and Proteins/genetics , Intracellular Signaling Peptides and Proteins/metabolism , Mice , Protein-Arginine N-Methyltransferases/antagonists & inhibitors , Protein-Arginine N-Methyltransferases/genetics , Repressor Proteins/antagonists & inhibitors , Repressor Proteins/genetics , Tumor Suppressor p53-Binding Protein 1ABSTRACT
Replication protein A is the major single strand DNA binding protein of human cells, composed of three subunits with molecular weights of 70, 32, and 14 kDa. Most of the DNA binding activity of RPA has been mapped to the largest subunit that contains two OB-fold DNA binding domains and a third, OB-like structure in the carboxyterminal domain (CTD). This third domain resembles an OB-fold with a zinc binding domain inserted in the middle of the structure, and has recently been shown to carry a coordinated Zn(II) ion. The bound metal ion is essential for the tertiary structure of the RPA70-CTD, and appears to modulate its DNA binding activity when tested with synthetic oligonucleotides. We show here that zinc strongly affects the conformation of nucleoprotein filaments formed between RPA and long natural DNA molecules. In these experiments, the CTD is dispensable for DNA binding and the unwinding of long double stranded DNA molecules. However, using band shift assays and electron microscopy, we found that RPA-DNA complexes contract at zinc concentrations that do not affect the conformations of complexes formed between DNA and a RPA70 deletion construct lacking the CTD. Our data suggest that nucleoprotein complexes with RPA in its natural, zinc-bearing form may have a compact rather than an extended conformation.
Subject(s)
DNA-Binding Proteins/chemistry , DNA/chemistry , Intermediate Filaments/chemistry , Nucleoproteins/chemistry , Protein Conformation/drug effects , Zinc/pharmacology , Bacteriophage M13 , Cations, Divalent , DNA Helicases/chemistry , DNA, Complementary/chemistry , DNA, Single-Stranded/chemistry , Electrophoresis, Agar Gel , Humans , Intermediate Filaments/ultrastructure , Microscopy, Electron , Nucleoproteins/ultrastructure , Replication Protein AABSTRACT
Replication protein A (RPA) is the major single strand-specific DNA-binding protein in eukaryotic cells. We have investigated the distribution of RPA in nuclei of proliferating HeLa cells and found that only one-third of the detectable RPA appeared to be bound to DNA in chromatin, whereas the remainder was free in the nucleosol. This distribution did not significantly change when cells were released from a double thymidine block into the S phase of the cell cycle. Single strand-specific endonucleases failed to mobilize RPA bound to chromatin in G1 phase and S phase HeLa cells. In contrast, brief treatments with pancreatic DNase I or with micrococcal nuclease sufficed to release RPA from its chromatin-binding sites. Sucrose gradient analysis of soluble micrococcal nuclease digests showed that the released RPA sedimented free of mono- or oligonucleosomal chromatin fragments, possibly indicating that most of the detectable RPA may be associated with chromatin sites, which are more open to nuclease attack than bulk chromatin. The surprising conclusion is that the majority of the detectable RPA is, either directly or indirectly, associated with double-stranded DNA regions in chromatin from HeLa cells in G1 phase and in S phase.
